600 54TH ST SW I Geotech Report 2025-01-29

GEOTECHNICAL INVESTIGATION EVERETT,WASHINGTON March 2,2018 8.1.3 Erosion and Sediment Control Erosion and sediment control(ESC)is used to reduce the transportation of eroded sediment to wetlands, streams,lakes,drainage systems,and adjacent properties. Erosion and sediment control measures should be implemented and these measures should be in general accordance with local regulations. At a minimum,the following basic recommendations should be incorporated into the design of the erosion and sediment control features for the site: • Schedule the soil,foundation,utility,and other work requiring excavation or the disturbance of the site soils,to take place during the dry season(generally May through September). However,provided precautions are taken using Best Management Practices(BMP's),grading activities can be completed during the wet season(generally October through April). • All site work should be completed and stabilized as quickly as possible. • Additional perimeter erosion and sediment control features may be required to reduce the possibility of sediment entering the surface water. This may include additional silt fences,silt fences with a higher Apparent Opening Size(AOS),construction of a berm,or other filtration systems. • Any runoff generated by dewatering discharge should be treated through construction of a sediment trap if there is sufficient space. If space is limited other filtration methods will need to be incorporated. 8.1.4 Foundation Design Proposed single-family residences may be supported on shallow spread footing foundation systems bearing on undisturbed medium dense or firmer native soils,re-compacted native soils,or on properly compacted structural fill placed on the suitable native soils. If structural fill is used to support foundations,then the zone of structural fill should extend beyond the faces of the footing a lateral distance at least 1/2 of the total depth of the overexcavation. The deepest areas of fill appear to be present in the area of building lots 2 through 5. In general,the fill thickness decreases to the north and east in this area. Moderate depths of fill are present in building lots 7 through 9 and in the detention tract. The fill in these areas is up to 4 feet deep and generally consists of native soils used as fill. Building lot io could not be explored due to topography and vegetation. Note that our estimates are based on the test pit explorations and do not necessarily fully describe the extent and depth of fill soils. Unless a deep foundation is considered for houses constructed over undocumented fill(rock columns, pipe piles,etc.),we recommend overexcavation and replacement of all unsuitable fill materials and loose native soils below foundation elements to the extent as described above. For shallow foundation support,we recommend widths of at least 18 and 24 inches,respectively,for continuous wall and isolated column footings supporting the proposed structure. Provided that the footings are supported as recommended above,a net allowable bearing pressure of 2,000 pounds per square foot(psf)may be used for design. 8